Conventionally, running control of an automated guided vehicle used for an automated guided vehicle system, which is intended to be automatized and laborsaving, generally employs a guidance system by fixed routes without tracks, which is advantageous in view of the cost and technology. Such fixed routes are determined by guidance lines, for example guidance tapes attached on the floor of an unmanned warehouse or a factory. An automated guided vehicle runs automatically along the guidance lines while detecting the guidance lines electromagnetically or by means of an optical system using a line detection sensor. Such guidance lines are generally formed as continuous or circular running routes and designed such that short-circuit running paths and charging areas are provided at several places along the route. At appropriate positions outside and along the circular guidance lines, a plurality of work stations are positioned for loading and unloading articles to be transported, and charging stations are positioned inside the circular path.
Furthermore, a plurality of automated guided vehicles are positioned on the above-mentioned guidance lines. When a transport request is given to an operation control unit from a factory host computer that controls factory facilities and work stations via a local area network (LAN), after running data and information related to the transport is given from the operation control unit by radio, these automated guided vehicles start running based on a start instruction to conduct an instructed transport or work order.
Now, the conventional system of transmitting information between the operation control unit and the automated guided vehicle is a communication system in which the control part of the operation control unit is connected to a radio with a cable conformable to RS232C, the control part of the automated guided vehicle also is connected to a radio with a cable conformable to RS232C, and the radios communicate with each other, for example, with a SS radio system (spread spectrum system). The control part of the operation control unit transmitted a command to the radio with serial communication via the RS232C cable, and the radio of the operation control unit transmitted the command by radio with the SS radio system to the radio of the automated guided vehicle, and thus, the control part of the automated guided vehicle received the command from the operation control unit with serial communication via the RS232C cable.
FIG. 11 shows how information (command, status) is passed between an operation control unit and an automated guided vehicle and the contents of processing in a conventional transport start processing.
First, when a running data download (D/L) request is sent from an automated guided vehicle to an operation control unit, the operation control unit writes running data and additional information related to a transport into a memory and first transmits the running data to the automated guided vehicle. To confirm receipt of the running data, the automated guided vehicle sends a running data transmission acknowledgment to the operation control unit. Upon receiving this message, the operation control unit then transmits the additional information to the automated guided vehicle. To confirm receipt of the additional data, the automated guided vehicle sends an additional information transmission acknowledgment to the operation control unit.
Thus, the running data and the additional information are transmitted to the automated guided vehicle, so that the operation control unit sends a start instruction to the automated guided vehicle after confirming that the automated guided vehicle is ready to start. To confirm receipt of the start instruction, the automated guided vehicle sends a start instruction acknowledgment to the operation control unit and starts running. The automated guided vehicle runs from the present position to an instructed loading station in an empty state, receives an article to be transported in the loading station, transports this article to be transported to an instructed unloading station, and supplies the article to the station concerned. Thereafter, the automated guided vehicle sends a transport completion notice to the operation control unit, thereby completing the designated transport.
Next, it will be explained as to how an automated guided vehicle is controlled when entering an area where guidance lines are merged.
FIG. 12 shows how information is passed between an operation control unit and an automated guided vehicle and contents of processing in a conventional merging control processing.
When an automated guided vehicle intends to enter a merging area of guidance lines, first, the automated guided vehicle sends a start allowance request to an operation control unit. Upon receiving this message, the operation control unit confirms whether there is any other automated guided vehicle in the requested target area for entering other than the automated guided vehicle that issued the start allowance request. If there is no other vehicle, the operation control unit immediately sends a start allowance to the automated guided vehicle. On the other hand, in the case where there is an automated guided vehicle in the requested target area for entering other than the automated guided vehicle that issued the start allowance request, the operation control unit waits until the other automated guided vehicle exits the requested target area for entering, then stores that the automated guided vehicle that issued the start request will occupy the area concerned, and sends a start allowance to the automated guided vehicle.
However, in the conventional information transmission system, the amount of communication per unit time was small, and it took a lot of time until an instruction for operation was given to an automated guided vehicle. There was also a waiting time on the side of the automated guided vehicle, so that the transport capability of the automated guided vehicle was reduced disadvantageously.
For example, in the case of the conventional communication by way of RS232C, a data transmission rate was 9.6 Kbps, and it took about 3 seconds to transmit running data from the operation control unit to the automated guided vehicle and about 0.5 second for transmission of a start instruction, so that a total of about 3.5 seconds was required. Therefore, a waiting time of about 3.5 seconds was necessary from the time a transport is completed until the next transport starts.
Furthermore, for the operation control unit to access status data such as in trouble, in transport, in transfer, stopping, charging, under manual operation and standby stored in the memory of the automated guided vehicle and to update the content thereof could take 0.5 second per vehicle. When there are, for example, 20 units of automated guided vehicles, it would take about 0.5×20=10 seconds.
Furthermore, the automated guided vehicle runs from the time 20 units of automated guided vehicles intend to enter a designated area until a start allowance is given at an average distance L of L=20×0.5 sec×0.66=6.6 m by setting the speed of the automated guided vehicle to be 40 m/minute. Therefore, for conducting a blocking control to avoid collisions between the automated guided vehicles, it was necessary either to provide a confirmation section of at least about 6.6 m for communication to confirm whether it is allowed to enter just before entering the designated area, or to stop the automated guided vehicle every time at the entrance of the designated area to confirm whether it is allowed to enter so as to send a start instruction. Therefore, there was a problem of loss in area productivity due to the extra running space of the confirmation section, and there was also a problem of loss in time since the automated guided vehicles stopped at the entrance every time even if there was no other automated guided vehicle in the designated area.
Moreover, when the operation control unit tries to read a large volume of data such as manipulation records and operating records stored in the automated guided vehicle for analysis of troubles with the automated guided vehicle, it takes a long time for communication, so that the waiting time of the automated guided vehicle increased, which led to the deterioration of the transport capability.
Furthermore, in order to reflect the result of the above-mentioned trouble analysis to the automated guided vehicle, a built-in ROM of the automated guided vehicle in which the transport control software is stored needed to be exchanged. In this case, the ROM exchange was carried out by stopping the transport for each automated guided vehicle, so that it required a stop time for the automated guided vehicles and also work by manpower, during which the production line had to be stopped disadvantageously.
In addition, another problem of the conventional information transmission system was that processing (communication process) for radio communication was needed. Communication protocols had to be determined for respective communication data, so that every time the type of communication data increased, the communication protocols needed to be revised.
Furthermore, communication processes are required for both the operation control unit and the automated guided vehicle, and thus, it is necessary to make an investment in the development of software for each.
Furthermore, for achieving higher communication efficiency, the structure regarding software for communication processes had to be changed to a polling system of high-speed processing, a mutual competitive communication system or the like, which disadvantageously led to a more complicated structure.
Moreover, when the content of communication is to be changed, the communication protocols and the communication process need to be modified or added.